1. Field of the Invention
The invention relates to dynamically vulcanized thermoplastic compositions having improved adhesion properties and a process for preparing the compositions.
2. Description of Information Disclosures
In recent years, there has been a significant commercial interest in polymer blends which have a combination of both elastic and thermoplastic properties. These polymer blends have been given the generic designation of Thermoplastic Olefins ("TPO"). They exhibit some of the properties of a cured elastomer as well as the reprocessability of thermoplastic resins. The elastomeric characteristics are enhanced if one component of the blend is a vulcanizable elastomer which is wholly or partially crosslinked.
The earliest work in the curing of TPO compositions was by Gessler and Haslett; see U.S. Pat. No. 3,037,954. That patent teaches the concept of "dynamic curing" wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer cured while continuously mixing and shearing the polymer blend. The result is a micro-gel dispersion of cured rubber in an uncured matrix of resinous thermoplastic polymer. Gessler's U.S. Pat. No. 3,037,954 discloses compositions comprising polypropylene and a rubber wherein the rubber may be, butyl rubber, chlorinated butyl rubber, polybutadiene, polychloroprene and polyisobutene.
U.S. Pat. No. 4,340,684 discloses a blend of a crystalline 1-olefin polymer, a styrene-butadiene rubber and a highly saturated elastomer. The highly saturated elastomer may be an ethylene-vinyl acetate copolymer (EVA). The compositions may be partially cured under dynamic conditions (col. 8, lines 60 to 68).
U.S. Pat. No. 4,607,074 discloses dynamically vulcanized thermoplastic compositions comprising a polyolefin resin, an uncured rubber and a fully cured rubber. The polyolefin resin may be EVA or EVA may be included along with the polypropylene or polyethylene as the resin. A preferred composition includes polypropylene and ethylene-vinyl acetate as the polyolefin resin.
U.S. Pat. No. 4,210,579 discloses a thermoplastic mixture of ethylene-propylene polymer or ethylene-propylene-diene polymer, a crystalline polypropylene and ethylene-vinyl acetate (EVA).
U.S. Pat. Nos. 4,639,487; 4,851,468 and 4,894,408 also disclose dynamically vulcanized compositions comprising ethylene-vinyl acetate.
There is still a need to improve the adhesion properties of dynamically vulcanized compositions, particularly for adhesion to highly plasticized vinyl and to rigid polyvinyl chloride, when used, for example, for co-extrusion or coinjection molding with the vinyl plastic or for heat sealing to the vinyl plastic.
It has now been found that the adhesion properties of elastomeric thermoplastic compositions can be improved by dynamically vulcanizing a blend of specified polymers.